1. Field of the Invention
The present invention relates to a method for manufacturing an ink jet head for discharging small droplets of printing "ink" (hereinafter referred to as ink) used for a liquid jet (hereinafter referred to as an "ink jet") printing method.
2. Related Background Art
The noises generated in printing by use of the ink jet printing method are small enough to be negligible. Also, with the adoption of this method, it is possible to print at high speeds on sheets of so-called ordinary paper without any particular or special treatment of the paper. As a result, this printing method has been rapidly in wide use in recent years.
Now, among ink jet heads using this method, there is known an ink jet head of the so-called side-shooter type that discharges ink in the direction perpendicular to the substrate having energy generating elements formed on it for generating energy which is utilized for discharging ink. As one structural example of the side shooter type head, it is generally practiced to form the ink supply opening through the substrate having the energy generating elements arranged on the surface thereof. The ink supply opening is provided for supplying ink to the ink flow paths having the energy generating elements in them, respectively. As the formation method of this ink supply opening, there are known mechanical means, such as drilling; means for using optical energy, such as a laser; or means for using chemical methods, such as etching, among some others.
Of these means and method, anisotropic etching is well known as a chemical etching method. In other words, when an alkaline chemical etching is executed on a silicon substrate (wafer) having the crystal plane orientations of &lt;100&gt;, &lt;110&gt; planes, directional selectivity may take place as the etching progresses in accordance with the crystal plane orientations. Then, anisotropy becomes obtainable as between the depth (engraving) direction and the width (expanding) direction of the etching. For example, with use of a silicon substrate provided with the &lt;100&gt; plane of the crystal plane orientations, it becomes possible to control the width of ink supply opening just by the initial width of opening where the etching begins, because the depth direction is geometrically determined. More specifically, as shown in FIG. 2D or FIG. 2E, it is possible to obtain the bottom face that has become narrower with a surface (formed by etching) at an inclination of 54.7.degree. in the depth direction from the etching initiation surface. In this respect, therefore, with the thickness of the substrate 1 and the etching width being taken into consideration, control can be easily made as to the width of the opening on the side opposite to the etching initiation surface of the substrate, that is, the width of the ink supply opening. Here, in FIGS. 2A to 2E, reference numeral 1 designates a substrate; 2, an etching suspension membrane; and 3, the formation member of ink flow paths, respectively. Also, reference numeral 4 designates a mask layer formed by etching-proof material, and 5, an ink supply opening.
An alkaline chemical etching of the kind is, roughly speaking, conducted for a comparatively long time using its strong alkali. Then, conventionally, a silicon oxide or other dielectric membrane is used as the mask layer 4 of etching-proof material in order to carry out heat treatment.
Here, for the mask pattern formation on this mask material, the techniques conventionally used for patterning the silicon oxide or other dielectric membrane, may be used. For example, there is known a wet etching that uses a mixed solution of hydrofluoric acid and ammonium fluoride, a dry etching that uses reaction gas, or the like.
Also, for the execution of the anisotropic etching, attention should be given so as not to allow etching solution to be in contact with the plane (surface) on the side opposite to the etching initiation plane, as such contact this may create a problem. Here, some means should be provided, such as a jig that uses an O-ring or an etching-proof rubber resist for protection.
Now, with the anisotropic etching, its etching progress is not only directed toward the depth (engraving) direction, but also, toward the width (expanding) direction (hereinafter referred to as side etching). As a result, some of the silicon oxide serving as the mask layer formed by etching-proof material may, in some cases, remain floating in the form of overchanging or projecting eaves (as at 8 in FIG. 2C or in FIG. 2F). When an ink supply opening 5 is formed in such a manner, the eaves 8 that have been created by the side etching may be broken in the subsequent processes of recording head manufacture, such as assembling or fabrication following the post-processing of the formation of the ink supply opening 5. There is a risk that these broken eaves pieces may lead to the creation of dust particles.
Therefore, means should be provided to remove the silicon oxide which remains in the form of eaves 8 after the formation of the ink supply opening. Here, for the removal thereof, it is possible to use the same technique as the one adopted for patterning as described earlier, together with the removal of other portions of the silicon membrane. In this case, however, there is a possibility that the mixed solution of hydrofluoric acid and ammonium fluoride used for this technique may present a problem with respect to the plane (surface of the substrate) on the side opposite to the anisotropic etching initiation plane. Then, for protection, a jig or some other means should be used so as not to allow the mixed solution or reaction gas to be in contact with the surface of the substrate. Here, for this means, it may be possible to share the protection means used for the anisotropic etching applicable to the formation of the ink supply opening. However, for the application of this means, there is a need for the provision of protection to cover the edge portion of a wafer, and also, to cover even the circumference of the etching initiation plane side in order to prevent the etching solution from being spread to the reverse side of the substrate. As a result, the silicon oxide membrane on the portions covered by the protection member 6 on the anisotropic etching initiation plane, tend to remain as they are even in the removal process that uses the mixed solution or reaction gas described earlier. Each of such remaining portions may create steps eventually in the processing that follows the etching.
Now, the detailed description will be given as below with reference to FIGS. 2A to 2G.
When an ink jet head is produced by means of anisotropic etching, a problem is encountered as described earlier if etching solution is allowed to be in contact with the surface of the substrate on the side opposite to the etching initiation plane, because on the surface there are formed the energy generating elements for use of discharging ink and an orifice plate member, and others. Here, therefore, on the reverse side of the substrate 1 where the etching terminates, a membrane 2 that contains at least silicon nitride is filmed in order to enable the anisotropic etching to be suspended on this membrane 2. Then, after having processed the ink supply opening 5 by means of etching (see FIG. 2D), this membrane 2 is removed by means of plasma dry etching using reaction gas, such as CF.sub.4 gas, from the reverse side of the substrate as shown in FIG. 2E.
However, in the process of removing the membrane 2, the larger portion on the silicon surface 1A, where no silicon oxide membrane remains on the reverse side of the substrate, is etched by the aforesaid CF.sub.4 gas as shown in FIG. 2G. Thus, a step 7 is created between this etched surface 1A and the surface which is not etched due to the remaining silicon oxide 4 as described earlier.
Now, in this respect, when the substrate is cut and separated in the following ink jet head manufacture processes, water used for such cutting enters each of the steps, which causes the creation of dust particles in the flow paths of each head thus produced.